Video: Using light cache

In this video, we are going to be working with our interior room to create a global lighting solution using V-Ray's light cache engine. Now, although not generally recommended as a primary bounce engine, we are just going to follow the same procedure as we did with our irradiance mapping exercise, and see what kind of a GI solution we can create using Light cache's basic controls. So let's dive in, and first of all, turn on the V-Ray's GI systems. Up to the Render Settings window icon, pull that dialog up, into the Indirect Illumination tab, and we can enable the GI systems, and of course, we need to make certain we are focusing on Light cache by setting it as the Primary bounce engine, and turning off our Secondary bounces.

This course introduces the features of the V-Ray 2.0 rendering engine and demonstrates how to extend the range of Maya with its state-of-the-art tools, such as irradiance mapping, fur and hair textures and shaders, and stereoscopic 3D rendering. The course covers critical concepts such as creating basic materials, image sampling, color mapping, subdivs, and lighting, as well as the Render Elements, RT, and physical rendering workflows in V-Ray. Exercise files are included with the course.

Using light cache

In this video, we are going to be working with our interior room to create aglobal lighting solution using V-Ray's light cache engine.Now, although not generally recommended as a primary bounce engine, we arejust going to follow the same procedure as we did with our irradiance mappingexercise, and see what kind of a GI solution we can create using Light cache's basic controls.So let's dive in, and first of all, turn on the V-Ray's GI systems. Up to theRender Settings window icon, pull that dialog up, into the Indirect Illuminationtab, and we can enable the GI systems, and of course, we need to make certain weare focusing on Light cache by setting it as the Primary bounce engine, andturning off our Secondary bounces.

Now, the default Light cache settings that we now get are really designed to giveus a fairly decent level of quality from the system.But these settings are assuming that we are using light cache in its favoriteposition: as a Secondary bounce engine.In fact, if we take a render at this moment in time, you will see a couple ofthings become apparent.Firstly, we see that with the default Subdivs value of 500, the Light cacheengine does calculate the GI solution very, very quickly for us, but we can alsosee that, well, we have lots and lots of blotchy noise in the scene.

Hopefully, though, you have also noticed that we do have lots and lots of light.There is a big difference in the level of initial illumination we're gettinghere, as compared to our irradiance mapping only solution.This is because light cache rays don't just bounce once.Like photons from which the technology is derived, light cache rays, once shotinto an environment, will perform multiple bounces automatically, and they dothis very quickly indeed.In fact, this is light cache's big strength.

Now, to improve our current solution, what about following the same steps aswith our irradiance mapping exercise, and turning on our V-Ray rectangular light: sky_portal.Well, we can do that, so let's just select that particular light type in theviewport, and if we come into our Attribute Editor, we can, first of all, enable the light.Remember, of course, on the way down to the Skylight option, we need to turn onShadows, and then we can enable that Skylight option.We do want to come and save our initial render; we want to make comparisons aswe're going, and now we can see what that Skylight option will do for us.

Although we can see that we do get a little bit of an improvement -- wedefinitely tone down the contrast levels in our noise --we still have not really made a huge difference to what the solution is giving tous. But seeing as how we have only really increased our render time by onesecond, and we're getting a positive result --we have this focal point for our GI system -- we will leave our skylight portal enabled.Of course, perhaps the obvious thing to do to increase the quality of oursolution would be to come back to our Light cache controls, and increase our Subdivs value.Well, let's double it up to a value of 1000.

Again, let's save a render, and let's see how those changes will affect our solution.Well, we can see that we have definitely improved things. We have smoothed outour blotchiness; our noise a little bit, and we can see that because we haveswitched between our two renders.We still have got nowhere near the level that we would want for afinal quality solution.Truth be told, the subdivisions value, unless we increased it up to a value ofsomething around about the 5000 to 6000 mark, would not even begin to give us areasonably noise-free solution.

And, of course, by the time we are up to those subdivision levels, our rendertimes would be so long that they would not compare favorably with our previousirradiance mapping and light cache combined solution, so therefore, increasingthe subdivision values, just to get a reasonably decent solution, really doesn'tseem like the best way to go.We could try working with all the Light cache controls at our disposal.For instance, we could work with the Prefilter option.This is a way of just averaging samples together during the initial calculationof our light cache samples.

We could also work with our Filter samples value.This is a way of doing the same thing, but after the calculation of oursamples has taken place.So let's really crank this value up; let's work with our Filter samples, andsee what that would do.Of course, we want to save our render.You can see, we definitely do make an improvement as to how the noise islooking in the scene.Again, let's just make certain that we do a comparison.We've definitely averaged, or smoothed things out a little bit, but you can see,we're also losing detail in the scene, and this really is always the problem withany blurring or averaging operations, which is exactly what our Pre- andPost-filter operations are.

Really, averaging to such a high level between samples is not always going togive us a desirable end result.I am just going to set that value back to 5, and make another admission.Unfortunately, no matter what we do, short of using extremely high Light cachesubdivision values, we are always going to get a somewhat blotchy GI render fromthe Light cache system.As we stated earlier, Light cache is just not usually a very good choice as aPrimary bounce engine.Achieving a high enough quality lighting solution is always going to requiresignificantly higher render times than an irradiance map and light cache combined solution.

And, of course, we generally will lose out on any fine details that arefound in the scene.Picking out scene detail is definitely a weak spot for our light cache.There is, however, one trick that light cache can perform that evenirradiance mapping cannot.Light cache can be configured to work as a progressive path trace renderer.This, essentially, is a way to perfectly reconstruct and render the light energyfound in our scenes, and the beauty of it is that there are no parameters thatneed to be tweaked once we have got the initial system up and running.

We can show you how to do that very quickly.Let's come down in the Light cache controls to the Mode option.If we drop this down, you can see we have this Progressive path tracing modeavailable, and now all we need to do is come up to the Calculation parameters ofour Light cache rollout, and if we want a completely unbiased render from thesystem, we need to set our Sample size to 0.And now we're just going to be working with the subdivision controls tobasically determine the quality of our final render.Again, let's just save what we have here, and let's take a render.

Now, what you see may initially look like a typically ordinary light cache calculation.In fact, it isn't.What we are seeing here is the final rendered image.These are the pixels as they are being drawn in Maya's render view.Of course, because we have -- relatively speaking, in terms of progressive pathtracing -- a very low subdivisions value, we're getting a very noisy render back.But if we were to set this value to something like 15,000, we can come and showyou the render that we would get from that.

So if we just go to File > Open image, and if I just come into our assets folder,down to Chapter 04, you see we have this progressive path trace bitmap.Let's open that, and you can see, we get a very nice render indeed.Yes, there is still some noise detail in the scene that would need to be takencare of. We would need to increase our subdivision values to do that.Remember, of course, the V-Ray's Image sampling controls, and the DMC sampler wouldhave no effect here at all.Everything is controlled simply by that subdivisions parameter.

You can see lots and lots of nice occlusion detail, lots of fine detail in thegeometry being picked out, and the lighting is looking very natural and realistic indeed.In this video, we have spent a little bit of time working with our Light cache controls.We have seen how we can use them to affect the quality, the smoothness, of our GIsolution, and remember, everything we have looked at here is applicable to Lightcache as a Secondary bounce engine also.Time, now, to move on to our final GI system of this chapter; the finalsystem that we will look at, and really, we're going to take a look at howthe Brute force mode works.

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